I am not certain that many of the current Brimar tubes are made in the United Kingdom. I have heard, but cannot pin down, that some of their tubes are sourced from Russia and China, then tested to Brimar standards. If they pass, then they are rebranded as Brimar.
Consider what they write on this page:
http://brimaruk.com/about-us/brimar-...onic-products/
"Brimar thermionic products are dedicated to bringing you the best valves possible – we know this is a huge task and not one to be taken lightly but each time you purchase one of our electron tubes it brings us closer to manufacturing right here in the U.K." This statement was put out 18-24 months ago, so perhaps they have started manufacturing some tubes in the UK, but this info is difficult to verify.